The heart of a computer is a magnetic hard disk drive (HDD) which typically includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and/or write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The volume of information processing in the information age is increasing rapidly. In particular, HDDs have been desired to store more information in its limited area and volume. A technical approach to this desire is to increase the capacity by increasing the recording density of the HDD. To achieve higher recording density, further miniaturization of recording bits is effective, which in turn typically requires the design of smaller and smaller components, along with a reduction in the flying height of the head over the magnetic disk.
The reduction of magnetic spacing between the magnetic disk and the magnetic head is very useful for improving the recording density of a magnetic disk device, and a reduction of the clearance between the disk and head has made a significant contribution to increased recording density. In recent years, a technique for actively controlling clearance, such as thermal fly-height control (TFC) has become more frequently used with an exothermic resistor, for example placed within the magnetic head, using the thermal expansion of the magnetic head due to heat produced by the resistor. This together with lower clearances has contributed to a reduction in the magnetic spacing.
In the most recent application of TFC technology, TFC control is used to create contact between the magnetic disk and the magnetic head, enabling a method to be employed whereby minute clearances of less than a few nanometers can be stably maintained by slightly reducing the amount of electric power supplied to the TFC heater in this state.
From this advancement, high-sensitivity detection of contact between the magnetic disk and the magnetic head is absolutely vital to ensure stability of low clearance and to ensure reliability. With conventional magnetic disk devices, methods of detecting contact generally involve assessing vibration of the magnetic head due to the contact from the output fluctuations, monitoring fluctuations in the positioning signal due to frictional force of contact, or detecting additional fluctuations in the voice coil motor and the spindle motor. However, with these methods, contact is not directly detected, and since vibration may indicate secondary fluctuations, it is difficult to detect contact with high precision. Therefore, the precision of contact detection has become a significant limiting factor in achieving low clearances. As a result, there is a demand for a contact sensor with high sensitivity able to detect contact more directly.